超类

package equals;

import java.time.LocalDate;
import java.util.Objects;

public class Employee {
    //实例域
    private String name;
    private double salary;
    private LocalDate hireDay;
    //构造器
    public Employee() {
    }
    public Employee(String name, double salary, int year, int mouth, int day) {
        this.name = name;
        this.salary = salary;
        this.hireDay = LocalDate.of(year, mouth, day);
    }
    //get方法
    public String getName() {
        return name;
    }
    public double getSalary() {
        return salary;
    }
    public LocalDate getHireDay() {
        return hireDay;
    }
    //加工资
    public void raiseSalary(double byPercent) {
        double raise = salary * byPercent / 100;
        salary += raise;
    }

    public boolean equals(Object otherObject) {
        //1.判断this与otherObject是否引用同一个对象
        if (this == otherObject)
            return true;
        //2.检测otherObject是否为null
        if (otherObject == null)
            return false;
        //3.比较this与otherObject是否属于同一个类（equals语义在每个子类有改变）
        //如果子类都有统一的语义可以使用if(!(otherObject instanceof ClassName))
        if (getClass() != otherObject.getClass())
            return false;
        //4.奖otherObject转换为相应的类类型变量
        Employee other = (Employee)otherObject;
        //5.对所有需要比较的域进行比较，使用==比较基本类型，使用equals比较对象域，Arrays.equals(type[] a, type[] b)比较数组
        //Objects.equals(a, b):a和b都为null返回true，其中之一为null返回false；否则返回a.equals(b)
        return Objects.equals(name, other.name)
                && salary == other.salary
                && Objects.equals(hireDay, other.hireDay);
    }
    //返回对象的散列码
    public int hashCode() {
        //Objects.hash((int|long|short|byte|double|float|char|boolean) value)返回给定值的散列码
        //Objects.hash(Object a)如果a为null返回0，否则返回a.hashCode()
        //Objects.hash(Object ...objects)返回一个散列码，由提供的所有对象的散列码组合得到
        //Objects.hash(type[] a)计算数组a的散列码
        return Objects.hash(name, salary, hireDay);
    }
    //返回表示对象值的字符串，println方法也会直接调用，只要对象与一个字符串通过操作符“+”连接起来就会自动的调用toString方法，即x.toString和“”+x效果一样，一般为：类名+域值
    //数组使用Arrays.toString(),多维数组使用Arrays.deepToString()
    public String toString() {
        //getClass返回包含对象信息的类对象，内容被封装在Class类中。getName返回这个类的名字
        return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";
    }
}

子类

package equals;

import java.util.Objects;

public class Manager extends Employee {
    //特有域
    private double bonus;
    //构造方法
    public Manager(String name, double salary, int year, int month, int day) {
        super(name, salary, year, month, day);
        bonus = 0;
    }
    //get方法
    public double getSalary() {
        double baseSalary = super.getSalary();
        return baseSalary + bonus;
    }
    //设置奖金
    public void setBonus(double bonus) {
        this.bonus = bonus;
    }
    //重新定义equals方法
    public boolean equals(Object otherObject) {
        //在子类中重新定义equals，要在其中包含调用super.equals(other)
        if (!super.equals(otherObject))
            return false;
        Manager other = (Manager)otherObject;
        return bonus == other.bonus;
    }

    public int hashCode() {
        return super.hashCode() + 17 * new Double(bonus).hashCode();
    }

    public String toString() {
        return super.toString() + "[bonus=" + bonus + "]";
    }
}

测试

package equals;

public class test {
    public static void main(String[] args) {
        Employee Siri1 = new Employee("Siri", 10000, 2001, 9, 7);
        Employee Siri2 = Siri1;
        Employee Siri3 = new Employee("Siri", 10000, 2001, 9, 7);
        Employee Xiaodu = new Employee("Xiaodu", 20000, 2021, 9, 5);

        System.out.println("Siri1 == Siri2: " + (Siri1 == Siri2));
        System.out.println("Siri1 == Siri3: " + (Siri1 == Siri3));
        System.out.println("Siri1.equals(Siri3): " + Siri1.equals(Siri3));
        System.out.println("Siri1.equals(Xiaodu): " + Siri1.equals(Xiaodu));

        System.out.println("Xiaodu.toString(): " + Xiaodu);

        Manager Carl = new Manager("Carl", 15000, 2021, 9, 7);
        Manager Boss = new Manager("Boss", 15000, 2021, 9, 7);
        Boss.setBonus(5000);
        System.out.println("Boss.toString: " + Boss);
        System.out.println("Carl.equals(Boss): " + Carl.equals(Boss));

        System.out.println("Siri1.hashCode(): " + Siri1.hashCode());
        System.out.println("Siri3.hashCode(): " + Siri3.hashCode());
        System.out.println("Xiaodu.hashCode(): " + Xiaodu.hashCode());
        System.out.println("Carl.hashCode(): " + Carl.hashCode());
    }
}